1. Field of the Invention
The present invention generally relates to broadcast control systems, network elements, and switching node apparatus for Asynchronous Transfer Mode (ATM) networks. More particularly, the present invention relates to a broadcast control system for determining unique routes to deliver broadcast cells to every destination in an ATM network that provides broadcast connections between a service provider terminal and a plurality of client terminals. The present invention also relates to network elements and switching node apparatus where the above broadcast control system is implemented.
2. Description of the Related Art
In recent years, the ATM network technologies are of great interest as one of the most promising backbones that provide high-speed, flexible communications services suitable for handling various kinds of multimedia traffic, such as voice, data, image, and video, in an integrated way. In such an ATM-based multimedia network, a service provider terminal delivers requested data to a plurality of client terminals in fixed-length packets, or cells. In addition to user data, the network exchanges some control data between the provider and client terminals for network management purposes, and some researchers propose the use of broadcast cells to achieve this function.
While the ATM User-Network Interface (UNI) Specification V3.0, a protocol specification formulated by the ATM Forum, has reserved some specific values of virtual path and virtual channel identifiers (VPIs/VCIs) for broadcast signaling cells, it does not provide any explicit specifications about how to route them in the network. The latest version of the ATM UNI Specification is V3.1 at present (December, 1996), in which no revision has been made as to the usage of broadcast signaling cells since v3.0. That is, the present ATM Forum specifications require some predefined VPI/VCI values to be used to deliver broadcast cells, implying that every piece of equipment in the network, or network element, will transmit and receive broadcast signaling cells through some common virtual channels.
FIG. 39 shows an example of a conventional ATM network which provides broadcast services. This network is organized by five ATM network elements 101 to 105 and a service provider terminal 106 connected to the ATM network element 101. Besides controlling delivery of cells over ATM transmission media, each of the ATM network elements 101 to 105 operates as a control system that manages its own client terminals (not shown in FIG. 39) that are directly connected thereto as ATM endpoint equipment. The service provider terminal 106 is a terminal that delivers various broadcast services via the ATM network to those client terminals, which services include news, weather forecasts, and other information necessary in daily life.
Suppose here that the service provider terminal 106 has sent broadcast cells to such an ATM network. Upon receipt of each broadcast cell, the ATM network elements 101 to 105 each terminate the received cell and deliver it to their respective local client terminals. Further, they relay the received cell to the next ATM network elements by repeating it toward all links except the one through which the cell was received, via a common ATM virtual channel (VPI/VCI). This repeating operation causes many same broadcast cells to be transmitted over the ATM network as indicated by arrows in FIG. 39.
The resultant unnecessary broadcast cells will fill the ATM network, which possibly causes network congestion accompanied by severe degradation in quality of services. Another problem with the conventional network is that a heavy workload will be imposed on the ATM network elements since they may receive the same broadcast cells many times.
Taking the above into consideration, an object of the present invention is to provide a broadcast control system and its component devices for determining unique routes to deliver broadcast cells to every destination in an ATM network so as to prevent it from network congestion and degradation in quality of service, as well as to reduce the amount of workload imposed on the network equipment.
To accomplish the above object, according to the present invention, there is provided a broadcast control system for controlling broadcast message distribution in an ATM network which is organized by a plurality of network elements and at least one service provider terminal connected to a source network element among the plurality of network elements. Here, each network element has a plurality of links that extend to other network elements, and the service provider terminal serves as a source of a broadcast cell.
This broadcast control system comprises the following elements:
(a) broadcast routing control cell transmitter, disposed in the source network element, for distributing a broadcast routing control cell containing reception link decision data to the plurality of network elements;
(b) control cell relaying unit, disposed in each of the plurality of network elements and activated when the broadcast routing control cell is received via one of the plurality of links, for modifying the reception link decision data contained in the received broadcast routing control cell, and transmitting the broadcast routing control cell with the modified reception link decision data through the plurality of links except for the one of the plurality of links used to receive the broadcast routing control cell;
(c) link selection and storage unit, disposed in each of the plurality of network elements and activated when a plurality of broadcast routing control cells have been received via different routes, for selecting a particular link from among the plurality of links, based on the reception link decision data contained in each broadcast routing control cell received, and storing a record of a combination of the particular link and the source network element which distributed the plurality of broadcast routing control cells; and
(d) broadcast cell relaying unit, disposed in each of the plurality of network elements, for receiving the broadcast cell through one of the plurality of links, identifying a network element that has distributed the broadcast cell, and transmitting the broadcast cell through the rest of the plurality of links if the link selection and storage unit has a record that matches with a combination of the network element identified as the sender of the broadcast cell and the one of the plurality of links that was used to receive the broadcast cell.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.